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GLUT Callback functions. Event-driven : Programs that use windows Input/Output Wait until an event happens and then execute some pre-defined functions according to the user’s input Events – key press, mouse button press and release, window resize, etc. GLUT Callback Functions.

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glut callback functions
GLUT Callback functions
  • Event-driven: Programs that use windows
    • Input/Output
    • Wait until an event happens and then execute some pre-defined functions according to the user’s input
  • Events – key press, mouse button press and release, window resize, etc.
glut callback functions1
GLUT Callback Functions
  • Callback function : Routine to call when an event happens
    • Window resize or redraw
    • User input (mouse, keyboard)
    • Animation (render many frames)
  • “Register” callbacks with GLUT
    • glutDisplayFunc( my_display );
    • glutIdleFunc( my_idle_func );
    • glutKeyboardFunc( my_key_events );
    • glutMouseFunc ( my_mouse );
event queue
Event Queue

Keyboard

….

Event queue

Mouse

MainLoop()

Window

Keypress_callback()

{

….

{

Mouse_callback()

{

….

{

window_callback()

{

….

{

rendering callback
Rendering Callback
  • Callback function where all our drawing is done
  • glutDisplayFunc( my_display);

void my_display (void )

{

glClear( GL_COLOR_BUFFER_BIT );

glBegin( GL_TRIANGLE );

glVertex3fv( v[0] );

glVertex3fv( v[1] );

glVertex3fv( v[2] );

glEnd();

}

idle callback
Idle Callback
  • Use for animation and continuous update
  • glutIdleFunc( idle );

void idle( void )

{

t += dt;

glutPostRedisplay();

}

user input callbacks
User Input Callbacks
  • Process user input
  • glutKeyboardFunc( my_key_events );

void my_key_events (char key, int x, int y )

{

switch ( key ) {

case ‘q’ : case ‘Q’ :

exit ( EXIT_SUCCESS);

break;

case ‘r’ : case ‘R’ :

rotate = GL_TRUE;

break;

}

}

mouse callback
Mouse Callback
  • Captures mouse press and release events
  • glutMouseFunc( my_mouse );

void myMouse(int button, int state, int x, int y)

{

if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN)

{

}

}

opengl geometric primitives
OpenGL Geometric Primitives
  • The geometry is specified by vertices.
  • There are ten primitive types:
vertices and primitives
Vertices and Primitives
  • Primitives are specified using

glBegin( primType );

glEnd();

    • primTypedetermines how vertices are combined

GLfloat red, green, blue;

Glfloat coords[3];

glBegin( primType );

for ( i = 0; i < nVerts; ++i ) {

glColor3f( red, green, blue );

glVertex3fv( coords );

}

glEnd();

an example
An Example

void drawParallelogram( GLfloat color[] )

{

glBegin( GL_QUADS );

glColor3fv( color );

glVertex2f( 0.0, 0.0 );

glVertex2f( 1.0, 0.0 );

glVertex2f( 1.5, 1.118 );

glVertex2f( 0.5, 1.118 );

glEnd();

}

vertices and primitives1
Vertices and Primitives
  • Points, GL_POINTS
    • individual points
vertices and primitives2
Vertices and Primitives
  • Lines, GL_LINES
    • pairs of vertices interpreted as individual line segments
vertices and primitives3
Vertices and Primitives
  • Line Strip, GL_LINE_STRIP
    • series of connected line segments
vertices and primitives4
Vertices and Primitives
  • Line Loop, GL_LINE_LOOP
    • Line strip with a segment added between last and first vertices
vertices and primitives5
Vertices and Primitives
  • Polygon , GL_POLYGON
    • boundary of a simple, convex polygon
vertices and primitives6
Vertices and Primitives
  • Triangles , GL_TRIANGLES
    • triples of vertices interpreted as triangles
vertices and primitives7
Vertices and Primitives
  • Triangle Strip , GL_TRIANGLE_STRIP
    • linked strip of triangles

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vertices and primitives8
Vertices and Primitives
  • Triangle Fan , GL_TRIANGLE_FAN
    • linked fan of triangles

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vertices and primitives9
Vertices and Primitives
  • Quads , GL_QUADS
    • quadruples of vertices interpreted as four-sided polygons
vertices and primitives10
Vertices and Primitives
  • Quad Strip , GL_QUAD_STRIP
    • linked strip of quadrilaterals

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vertices and primitives11
Vertices and Primitives
  • Vertices may be specified in 2D, 3D, or 4D.
  • 2D coordinates are promoted to 3D by assigning a Z value of zero.
  • 4D homogeneous coordinates are reduced to 3D by dividing x, y, and z by the w coordinate (if non-zero).
vertices and primitives12
Vertices and Primitives
  • Between glBegin/ glEnd, those opengl commands are allowed:
    • glVertex*() : set vertex coordinates
    • glColor*() : set current color
    • glIndex*() : set current color index
    • glNormal*() : set normal vector coordinates
    • glTexCoord*() : set texture coordinates
vertices and primitives13
Vertices and Primitives
  • glMultiTexCoord*() : set texture coordinates for multitexturing
  • glEdgeFlag*() : control drawing of edges
  • glMaterial*() : set material properties
  • glArrayElement() : Extract array element data
  • glCallList(), glCallLists() : execute display list
slide26
GLUI
  • GLUI is a GLUT-based C++ user interface library which provides controls such as
    • buttons,
    • checkboxes,
    • radio buttons,
    • spinners, etc.
  • It is window-system independent, relying on GLUT to handle all system-dependent issues, such as window and mouse management.
glui simple programming interface
GLUI - Simple Programming Interface
  • GLUI provides default values for many parameters in the API and there are several ways to create a control:

GLUI *glui;

...

glui->add_checkbox("Click me"); Adds a simple checkbox with

the name "Click me"

glui->add_checkbox("Click me", &state );

The variable state will now be

automatically update to reflect the state of

the checkbox (live variable).

glui->add_checkbox( "Click me", &state, 17, callback_fn );

Now we have a live variable, plus a callback function

will be invoked (and passed the value \'17\') whenever

the checkbox changes state.

usage for standalone glui windows
Usage for standalone GLUI windows

Integrating GLUI with a new or existing GLUT application is very

straightforward. The steps are:

  • Add the GLUI library to the link line (e.g., glui32.lib for Windows -lglui in Linux).
  • Include the file "glui.h" in all sources that will use the GLUI library.
  • Create your regular GLUT windows as usual. Make sure to store the window id of your main graphics window, so GLUI windows can later send it redisplay events:

int window_id = glutCreateWindow( "Main gfx window" );

  • Register your GLUT callbacks as usual (except the Idle callback, discussed below).
usage for standalone glui windows1
Usage for standalone GLUI windows
  • Register your GLUT idle callback (if any) with GLUI_Master (a global object which is already declared), to enable GLUI windows to take advantage of idle events without interfering with your application\'s idle events. If you do not have an idle callback, pass in NULL.

GLUI_Master.set_glutIdleFunc( myGlutIdle );

or

GLUI_Master.set_glutIdleFunc( NULL );

  • In your idle callback, explicitly set the current GLUT window before rendering or posting a redisplay event. Otherwise the redisplay may accidently be sent to a GLUI window.

void myGlutIdle( void )

{

glutSetWindow(main_window);

glutPostRedisplay();

}

usage for standalone glui windows2
Usage for standalone GLUI windows
  • Create a new GLUI window using

GLUI *glui = GLUI_Master.create_glui( "name", flags, x, y );

Note that flags, x, and y are optional arguments. If they are not specified, default values will be used. GLUI provides default values for arguments whenever possible.

  • Add controls to the GLUI window. For example, we can add a checkbox and a quit button with:

glui->add_checkbox( "Lighting", &lighting );

glui->add_button( "Quit", QUIT_ID, callback_func );

usage for standalone glui windows3
Usage for standalone GLUI windows
  • Let each GLUI window you\'ve created know where its main graphics window is:

glui->set_main_gfx_window( window_id );

  • Invoke the standard GLUT main event loop, just as in any GLUT application:

glutMainLoop();

  • Refer GLUI Manual on the usage for GLUI subwindows
references
References
  • http://www.opengl.org/documentation/spec.html
  • The OpenGL Programming Guide - The Redbookhttp://www.opengl.org/documentation/red_book_1.0/
  • http://www.cs.rit.edu/~jdb/cg1/openGLIntro.pdf
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